The purpose of this project is to assess the neuropsychiatric status of HIV-positive individuals who have abused drugs over a long period of their lives. There exist very little data on the impact of drug use on the brain structure and on the cognitive status of HIV positive individuals. This protocol will include 60 HIV positive participants who do not show any overt signs or symptoms related to AIDS. Data collected from the HIV positive individuals will be compared to 60 matched seronegative individuals with similar drug history. We will test the hypothesis that HIV status might exacerbate the neurological status of drug using individuals. These might be reflected in cortical and subcortical structural abnormalities, vascular abnormalities, as well as neuropsychological decrements. A battery of psychological tests was designed to provide information about demographics, drug use, neurocognitive measures, and personality structures. Data obtained from this battery will be correlated with volumetric measures of the brain structure, as determined by high resolution MRI scans. Participants are undergoing: 1) a complete neurological examination, 2) a D.I.S. interview, 3) a battery of neuropsychological tests, 4) sensory testing, 5) EEG, 6) Transcranial Doppler, and 7) MRI scanning.